Non-stick surface involves substrate modification and/or treatment so as to reduce the ability of materials to stick on it. Various compositions that generally have high viscosity like food preparations e.g tomato ketchup to personal care preparations like shampoo, liquid soap, moisturizing lotions etc., are packaged in containers. The material wastage due to sticking of materials or contents in a container to its walls is enormous.
One of the most commonly employed and commercially practiced approach for fabricating non-stick surfaces is the use of polytetrafluoroethylene (PTFE or Teflon) coating. However, this process is expensive and poses both environmental and health concerns.
U.S. 20110069361 (Jun Hyun-Woo et al.) discloses different ways to create pattern or imprint through either etching or injection moulding or hot embossing for making superhydrophobic surface. This has limited application as the contact angle obtained would not be very high since the process will form only micropillars, consequently the hydrophobicity imparted by such treatment would be lower.
Use of hydrophobic particles of one or more sizes and their combinations have been disclosed in WO12138992 (Trustees of Univ. of Pennsylvania), to create transparent hydrophobic surfaces. Use of combination of particles with different particles sizes results in enhanced roughness, which in turn enhances the hydrophobic properties.
However, these particles do not strongly bind to the surfaces, hence they cannot withstand damage to the surface, and subsequently the water repellence property is lost.
To circumvent this problem, use of binders (U.S. 2012107581, US Dept. of Energy) or coupling agents (WO14038701, Toppan Printing Co. Ltd) have been proposed. U.S. 2012107581 discloses a composition for producing an optically clear, well bonded superhydrophobic coating which includes hydrophobic particles, a binder and a solvent. They use ethyl cyanoacrylate, polyacrylic acid, polytetrafluoroethylene, polyurethane as the binder. In such cases, low concentrations of binders are typically mixed with the particles and multiple dip cycles are required to achieve superhydrophobicity. Alternatively, use of coupling agents has been disclosed in WO14038701 but they do not generate micropillars and the process employed is different.
U.S. 2001/0051273 A1 (Veerasamy) discloses a substrate coated with a hydrophobic layer(s) that includes e.g., highly tetrahedral amorphous carbon that is a form of diamond-like carbon (DLC), or any other suitable material. The exterior surface of the resulting coated article exhibits a surface roughness sufficient so that the article has an initial contact angle of at least about 100 degrees. In certain embodiments, the layer has a surface energy of no more than about 20.2 mN/m and/or an average hardness of at least about 10 GPa.
The problem with the above mentioned methods for making surfaces hydrophobic is that either the surfaces cannot withstand damage even by mild abrasion and subsequently the water repellence property is lost or the resulting contact angle is relatively low. This is mainly due to dislodging of the hydrophobic particles from the surface. The present inventors have been able to select adhesives that allow strong adherence of particles to the surface to provide good and stable hydrophobic properties. It is a challenge to obtain stable super hydrophobic surfaces and the present inventors have been able to achieve this by a specific process and by a combination of creating micropillars along with the use of specific adhesives and hydrophobic particles.
It is an object of the present invention to provide a process to modify the surface of an object to make the surface non-sticking and thus provide an easy flow for viscous materials.
It is another object of the present invention to provide a process to modify the surface of an object to provide super hydrophobic surfaces by creating micropillars and depositing hydrophobic particles using an adhesive layer.
It is another object of the present invention to provide a process to modify the surface of an object to make the surface hydrophobic and to retain this property even when the surface is subjected to damage by mild abrasion.